1. Field of the Invention
This invention is in the field of vacuum filters including a rotatable drum which has a foraminous filter surface thereon. There are provided an arcuate jacket in spaced parallel relation to a portion of the periphery of the drum, and divider means to divide the jacket into two superposed chambers. One of the chambers is connected to a source of steam and the other is in open communication with the filter surface.
2. Description of the Prior Art
Slurries which occur in the preparation of coal in large quantities could previously be utilized with efficient economic results only when it was possible to mix the coal slurries after being reduced to approximately a 20 to 25% water content with coking coal. There was a limit, however, on this kind of an operation because the water content of the coal could not be increased as much as desired. In other cases, the dehydrated coal slurry had to be applied as a fuel of lesser quality with appreciable losses.
In order to bring down the water content of the slurries as much as possible, it has been suggested to employ suction filters for the production of a filter cake which was removed and subjected to infrared radiation, whereupon the filter layer was raised to the apex of the filter drum, turned and further dried. Such a method is described in German Pat. No. 1,015,412. With this method, however, the water content of the filter cake was diminished only slightly, and the investment expenditure for this equipment was quite high.
In German Laid Out Specification No. 1,177,572 there is described a method for the dehydration of coal slurries with vacuum drum or vacuum disc filters, wherein water vapor at a raised temperature and with a predetermined pressure is conveyed to a previously dehydrated filter cake. The water vapor pressure was so adjusted that the condensation point of the steam penetrating into the previously dehydrated filter cake existed directly above the filter. The utilization of this method in practice, however, established that the superheated steam temporarily or intermittently condensed on the surface of the filter cake or on the inner walls of the filter drum assembly, and the condensate deposited itself particularly in the areas of the removal apparatus, so that the water content of the cake was again increased to an undesirable extent.